GUEST, Another... has it. It's not the competition, which is healthy for kids. Arguably, the lack of competitive activity during schooling in the UK appears to be contributing to vandalism, social problems and unemployability among teenagers.
It's when parents take it too seriously (displacement for their own ambitions in that respect?). I see it all the time with other parents when my lad competes in athletics, also with my nephew and "tennis mums." I have been at a number of athletics competitions where the child gets berated for lack of technique / training / whatever by a parent weighing about 20 stone, in a tracksuit and trainers, stuffing their face with crisps or chips!